lkml.org 
[lkml]   [2018]   [Dec]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] x86/speculation: Add support for STIBP always-on preferred mode
Date
On 12/11/2018 04:22 PM, Borislav Petkov wrote:
> On Tue, Dec 11, 2018 at 10:17:30PM +0000, Lendacky, Thomas wrote:
>> If using just SPECTRE_V2_USER_STRICT then the code in stibp_state() would
>> have to be able differentiate between the case where the mode was switched
>> because of X86_FEATURE_AMD_STIBP_ALWAYS_ON vs a kernel command line with
>> "spectre_v2_user=on". I could always set and use a static variable in the
>> file just for the stibp_state() case.
>
> Does it matter on X86_FEATURE_AMD_STIBP_ALWAYS_ON CPUs?
>
> I mean, we want STIBP to be always on there so you can do:
>
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 25e914f77bb8..d14860d1cf9c 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1089,7 +1089,10 @@ static char *stibp_state(void)
> case SPECTRE_V2_USER_NONE:
> return ", STIBP: disabled";
> case SPECTRE_V2_USER_STRICT:
> - return ", STIBP: forced";
> + if (boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
> + return ", STIBP: always on";
> + else
> + return ", STIBP: forced";
> case SPECTRE_V2_USER_PRCTL:
> case SPECTRE_V2_USER_SECCOMP:
> if (static_key_enabled(&switch_to_cond_stibp))
>
> so if user has booted with spectre_v2_user=on, we say, "oh well, it is always
> enabled anyway"... or?

I'm ok with that. Having said that, we can probably just leave it as is
and return "forced" even for the ALWAYS_ON case, then.

But if we want to differentiate, though, a simple static bool that is set
when the mode is switched works just as well.

>
>> I'll give it a bit of time and see if there's any other discussion and
>> re-submit without the new SPECTRE_V2_USER_STRICT_PREFERRED value.
>
> Sure.

Eh, I'll just submit v2 with the changes now and we can decide between the
above or the bool.

Thanks,
Tom

>
\
 
 \ /
  Last update: 2018-12-11 23:46    [W:0.077 / U:1.344 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site